Voluntary demand for carbon offsetting grew 4% in 2012, when buyers committed more than $523 million to offset 101 million metric tonnes of greenhouse gas emissions. Private sector buyers flocked to offsets earned by planting trees, saving tropical forests, or distributing clean cookstoves in the developing world, according to this year’s State of the Voluntary Carbon Markets report, released by Forest Trends’ Ecosystem Marketplace this week in Barcelona, Spain.

The European private sector, including regulated energy utilities, was the market’s biggest voluntary buyer – seeing demand grow 34% to 43.4 million tonnes of offsets even in the face of significant challenges to Europe’s mandatory carbon market.

Across the pond, United States-based corporations, ranging from The Walt Disney Company to Chevrolet, offset more emissions than buyers in any other single country at 28.7 million tonnes. A little over a third of offsets purchased by US buyers (9.7 million tonnes) were obtained for future use in California’s emerging cap-and-trade program.